Patent ES-316873-A1 (ES)
Title: Improvements in or relating to hydraulic control mechanisms
IPC: B62D11/08
Filed: 1965-08-27
Abstract: Each track of a crawler tractor is propelled through a shaft 1, brake drum and clutch device 2, reduction gearing 4 and driving sprocket 5, the pair of tracks being driven from the vehicle engine through a main clutch and transmission gearing, not shown. Each brake/clutch device comprises a band brake 6 actuated by an hydraulic ram 7 and a multi-plate clutch actuated by an hydraulic ram 9, the rams 7 and 9 being operated from a single manual control device 11, 12. The control devices for each track mounted in a common valve chest 13 each comprises a valve spool 12, Fig. 3, operating within a tubular nember 39 having galleries 40-45 and ports 46-51 with which co-operate lands 55 to 58 on the spool. Fluid is supplied from a connection 62, Fig. 4, past a damped relief valve 64 to a duct 68 from which lead ports 69, 70 and 71. Port 69 is connected via a check valve to gallery 40, and port 70 is connected to gallery 43. The port 71 is connected to a gallery 53 and drain passage 75. Galleries 42 and 45 are connected to a compartment 77 which drains to reservoir and galleries 41 and 44 are connected, respectively, through connections 78 and 79 with the brake and clutch actuating cylinders 7 and 9. Land 55 is provided with an axial leak path 54 so that fluid pressure may act upon the end face of spool 12. In operation, the spool 12 is moved downwardly against the pressure of spring 59, the drain galleries 51 and 53 first being closed so that pressure builds up in duct 68, and then ram 9 is actuated so as to disengage the clutch, by connecting ports 49 and 50, the brake port 47 and drain port 48 still being in communication. Further movement of the spool holds the clutch disengaged and applies the brake by bringing ports 46 and 47 into communication. A circlip 60 on the spool 12 coacts with an abutment 61 to limit the upward movement of the spool. In a modification, Fig. 6, the fluid supply connection 62 and supply duct 68x register with an annulus in a valve spool 80 which is located in a bore connected by a passage 87 to reservoir and is urged against a shoulder 88 by a spring 82. An additional passage 86 connects the valve bore to the supply passage 68. Pressure in the space 81 above the spool 80 is maintained equal to that of the fluid supply by a small bore 84, but in the event of sudden build up of pressure, the valve spool 80 moves upwardly thereby connecting the ducts 86 and 87 causing collapse of pressure in the duct 68x. A cone valve 89 is unseated during this operation, but after pressure equalization, is reseated and the valve 80 again seats on the shoulder 88. The multi-plate clutch comprises a drum 2 forming a seating for the band brake 6 and to which one series 19 of clutch discs is fixed. An interleaved series of clutch discs 20 is connected to a member 22 and the discs are held in engagement by compression springs 23 acting between a pair of pressure plates 21 and 25. A thrust member 28, which, by axial movement can disengage the clutch discs, is connected by thrust pins 29 to a collar 30 which is journalled in a bearing 32 and is carried by and can move axially on the flange member 27 mounted on the input shaft 1. The bearing 32 is itself trunnioned in a frame member 36 which is journalled in the transmission housing to one side of the shaft 1 and has a short arm 38 affixed thereto which is caused to turn by an hydraulic ram and thereby apply pressure between the thrust plates 25 and 28 to disengage the clutch.